It is often a requirement to place an energy applicator in an area where the surrounding media may change with time and/or application of power. This occurs, for example, in soil remediation and heating of viscous oil deposits, where the applicator may be surrounded by air, gas, water, or hydrocarbons, individually or in mixtures. The transmission of substantial amounts of microwave power is most efficiently done by a waveguide. However, this requires sealing and pressurization of itself and the applicator to prevent inflow of the items being heated.
The previous approaches have used slotted waveguide applicators. Slots are typically on the broad wall of the waveguide. See, for example, W. Rueggeberg in “A Multislotted Waveguide Antenna for High-Powered Microwave Heating Systems”, IEEE Transactions on Industry Applications, Vol. 1A-16, Number 6, pp 809-813, November/December 1980.